The prior art includes a method for transmitting two-dimensional information, which comprises the steps of decomposing an image being transmitted element by element, subsequent time or phase modulation of a coherent light flux in accordance with the successive elements of the decomposed image as the image is being scanned, transmission of the time-modulated light flux through an optical communication line, demodulation thereof as it is being received, and reproducing a visible image.
The foregoing method is disadvantageous in that the transmission of two-dimensional information involves decomposing, element by element, the image being transmitted. As a result, it takes a substantial amount of time to transmit a complete two-dimensional image.
The prior art includes a system for transmitting two-dimensional information according to the foregoing method, which comprises means and units arranged along the path of the coherent light flux, said means and units including a coherent light source, an amplitude or phase modulator which modulates the light flux in time in accordance with a useful signal formed in a unit for decomposing element by element, the two-dimensional image being transmitted, a communication line which is free space, and receiving means for the demodulation of received signals and reproduction of a visible two-dimensional image.
The foregoing system is disadvantageous in that it takes a substantial amount of time to transmit a two-dimensional image, because at each given moment the signal being transmitted carries information only on one element of the decomposed image that is being transmitted. In addition, no provision is made in this system for compensation of distortions due to variable nonuniformities of the medium in which the information-carrying light flux travels.
The prior art also includes a system for transmitting two-dimensional information in accordance with the above-mentioned method, wherein the medium for propagation of time-modulated light signals is a glass, fiber-optic light guide.
This system has the same disadvantages as the one in which free space is used as the light signal propagation medium. It should also be added that glass, fiber-optic light guides are marked by great signal attenuation.
The prior art includes still another system for transmitting two-dimensional information in accordance with the above-mentioned method, wherein the function of the medium for propagation of time-modulated light signals is performed by a light pipe with a number of beam-guiding lenses or mirrors.
The foregoing system has the same disadvantages as the one where free space serves as the medium for propagation of light signals.
In addition, all the above systems prove to be very expensive in transmitting information over long distances.
The prior art further includes a method for parallel transmission of a two-dimensional image over a distance of up to several meters, wherein amplitude modulation of a light flux is carried out by means of a bundle of wavebeam guides, each of these guides transmitting a light signal corresponding to a separate element of a decomposed image being transmitted.
The prior art includes a system for parallel transmission of two-dimensional images in accordance with the foregoing method, which comprises means and units successively arranged along the path of a light flux, these means and units including a light source, a unit for light signal modulation, a bundle of light guides whose number must correspond to that of the elements of a decomposed image being transmitted, and receiving means to ensure visual observation of, or to record, the image being transmitted.
The latter prior art method and system for parallel transmission of two-dimensional images have the following disadvantages:
great signal attenuation in transmitting over long distances;
difficulties involved in joining together light guides at the input and output of the communication line;
impossibility of spatial phase modulation of the light flux;
difficulties involved in maintaining communication among a great number of subscribers.